Electrode steam boiler apparatus



United States Patent 3,187,160 ELECTRODE STEAM BOILER APPARATUS Gerald Austen Williams, Harrow, England, assignor to Bastian and Allen Limited, Harrow, England, a company of Great Britain Filed Jan. 10, 1962, Ser. No. 165,446 Claims priority, application Great Britain, Jan. 12, 1961, 1,384/61 4 Claims. (Cl. 219286) This invention relates to electrode steam boilers of the type in which the boiler load and/ or the pressure of the delivered steam is controlled by adjusting the Water level in the boiler.

The displacement of water from the boiler to lower the water level in the boiler is usually achieved in one of two ways. In the first of these the boiler is in communication with a balance tank whose contents are at substantially the same pressure as those of the boiler. In order to transfer water from the boiler to the balance tank or vice versa there must be a pressure ditferential and there is therefore no control available when there is no pressure within the boiler as, for example, during the initial starting period or during periods of high steam demand. In some cases, adjustment is achieved by bleeding steam from the balance tank but even this may not be sufiicient to transfer the required amount of water in the case of a heavy demand of steam from the boiler itself, and is not possible when the system is cold and there is no steam in the boiler.

In the second system, the water displaced from the boiler is transferred to the feed tank which is at atmospheric pressure. The motive power for this transfer will be the steam pressure in the boiler when this exists or gravity when the boiler is not under pressure. In this system water at an elevated temperature corresponding to the steam pressure within the boiler is discharged into the feed tank where it flashes into steam. The system is therefore inefiicient. Moreover, when the feed tank becomes overheated and it approaches boiling point the feed pump may find it diflicult to handle the feed water due to cavitation on the suction side of the pump. In addition the control valve between the boiler and the feed tank and, to a lesser extent, the feed pump and its associated valve will have to handle water with a higher proportion of impurities than the make-up water supply and this may lead to a high rate of scale deposition on these parts.

The present invention combines the advantage of both the above methods and gives more complete control than the balance tank system without the discharge of hot water to the feed tankat atmospheric pressure as in the second system.

Electrode steam boiler apparatus comprises, according to the first aspect of the present invention, an electrode steam boiler of the type specified, a closed container the top of which is connected to the boiler at a point in the boiler which is always submerged during normal operation of the boiler, and aperture means at the bottom of the container through which water can be withdrawn from the container and through which water can be pumped into the container.

The method of operating the electrode steam boiler aplrparatus of the first aspect of the invention, which itself forms the second aspect of the invention, comprises maintaining the container full of water and controlling the supply of water to and the withdrawal of water from the bottom of the container in accordance with the load on the boiler and/or the pressure of the steam supplied by the boiler.

Thus when the boiler has been operated at high load and it is required to operate at a lower load, water is withdrawn from the bottom of the container and may be passed to a point at atmospheric pressure, for example the feed tank. The water displaced from the boiler, still at boiler pressure, will pass into the container where it may be stored until it is required again. Preferably the container is lagged to reduce heat loss from the contents of the container to a minimum. The Water which is removed from the container will be cold and will never have passed into the boiler and consequently will not contain the high concentration of impurities that the boiler water may contain. The water removed from the container will have been in contact with the hot boiler water over only a comparatively small cross sectional area and, because of the low thermal conductivity of water and the thermal Stratification which occurs, there will be only a small amount of physical mixing and of transfer of heat between the hot and the cold water. If the demand on the boiler again increases the feed pump will pump cold water into the bottom of the container and the water in the container will be returned to the boiler.

The container may take various forms. In one arrangement, the container is constituted by the lower part of the boiler shell and is separated from the steam generating part of the shell by a substantially horizontal baflie having in it an aperture through which the container is in communication with the steam generating part. However, in the preferred arrangement, the container is external of the boiler and comprises a cylinder with its axis approximately vertical. In another possible construction the container may take the form of a coiled pipe with the axis of the coil approximately vertical.

The quantity of water displaced from the boiler by a change from maximum to minimum rate of operation of the boiler will vary depending on the conductivity of the water in the boiler and hence on the concentration of impurities but preferably the container has a capacity approximately equal to the maximum amount of water displaced by a change from maximum to minimum rate of operation of the boiler. In a preferred arrangement, the aperture means are connected to a pipe which contains a feed pump and to a pipe which contains a control valve and communicates with a point at atmospheric pressure, for example the feed tank. The aperture means may be connected to a single pipe which branches into the pipe containing the feed pump and the pipe controlling the control valve. The structure by means of which the above-mentioned and other advantages of the invention are attained, will be fully described in the following description, taken in conjunction wtih the accompanying drawings showing two preferred illustrative embodiments of the invention, in which:

FIGURE 1 is a schematic diagrammatic representation of an electrode steam boiler apparatus embodying the invention, and

FIGURE 2 is a schematic diagrammatic representation of the illustrative electrode steam boiler apparatus embodying the invention.

The apparatus shown in FIGURE 1 of the drawing includes a boiler shell 10 containing three electrodes 11 to which power is supplied from a three-phase supply through leads 12. Feed water is supplied to the boiler from a feed tank 13 by a feed pump 14 in a pipe line 15 which leads from the feed tank 13 and opens into the boiler shell 10 at a point below the bottom of the electrodes 11. Non-return valves 16 and 17 are provided in the pipe line 15 on either side of the feed pump 14. The pipe line 15 includes a cylindrical container 18 which has its axis vertical, part of the pipe-line 15 connecting the boiler 10 to the top of the container and the remainder of the pipe line 15 extending from an aperture in the bottom of the container to the feed tank 13.

Branching off from the pipe line 15 between the feed pump 14 and the container 18 is a pipe line 19 which leads to the fed water tank 13 and contains a solenoid-operated valve 20. The solenoid of the valve 20 is energised through a line 21 containing a pressure control switch 22 and a load control'relay 23 which is controlled from a coil 24 around one of the leads 12.

The boiler is controlled by adjusting the Water level in the boiler to vary the depth of the electrodes 11 immersed in the water. The range of control is between the level A at'which the electrodes are substantially fully immersed and level B at which no part of the electrodes is immersed and the load is zero. The volume which the container 18 can hold is equal to the volume of water required to alter the water level in the boiler from level B to level A.

The method of control of the boiler is similar to those conventionally used and may be as follows. The feed pump 14 runs continuously. When valve 20 is closed, the rate of supply of water to the boiler is equal to the pump output. When valve 20 is fully open its flow capacity is greater than the delivery capacity of the pump. Thus, the water pumped by the pump passes straight back to tank 13 through valve 20 and water from container 18 also passes through valve 21 Water will pass from the container 18 chiefly because of the pressure in the boiler but also by gravity. From the drawing it is seen that the minimum water level B in boiler is above the level of water in said tank 13. The load control relay 23 is closed during normal operation with the valve being modulated by the pressure control switch 22 to match the steam demand. Thus if the steam demand should fall, the valve 20 will be opened and water bled from the container 18 to the fed tank 13. A corresponding amount of water will flow from the boiler to the container 18. When demand rises again the valve 20 is closed and the feed pump 14 pumps water into the container 18 and a corresponding amount of water flows from the container 18 into the boiler 10. a

The container 18 is lagged to prevent so far as is possible loss of heat from the container. Hot water displaced from the boiler enters the top of the container 18 and will tend to remain there and is in contact with cold water pumped in by the feed pump only over the horizontal cross section of the container as represented by the line C. Only a little mixing will take place and it will be the hot water which is contained in the upper part of the container 18 which Will pass into the boiler shell when cold water is poured into the bottom of the container. Similarly when the valve 26 is openedit is cold water from the lower part of the container 18 which will pass to the feed tank 13. Thus it will be seen that in the apparatus according to the invention the feed pump 14 and the control valve 20 only handle water which has not'had its temperature and impurities content increased by being mixed with water from the boiler; also, hot water from the boiler is not discharged to a point at lower pressure but it is merely stored at boiler pressure until it is required again. I

In the modification shown in FIGURE 2 the general arrangem ent is similar to that shown in FIGURE 1 and will not be described again. However, the container 18 of the apparatus shown in FIGURE 1 is replaced by a container within the boiler shell which is separated from the boiler proper containing the electrodes by means of a horizontal baflie 30 having a small aperture 31 through which the container and the boiler proper are in communication.

What I claim as my invention and desire to secure by Letters Patent is:

Cir

1. Electrode steam boiler apparatus comprising a boiler, steam generating electrodes in the boiler, a closed container having an upper end and a lower end, said container having a volume substantially equal to the volume of water contained between minimum and maximum levels of said boiler during normal operation, passage means connecting the upper end of said container to said boiler at a point below the minimum water level during normal operation, a feed pump connected to a water source, passage means connecting the discharge side of said fed pump to the bottom end of said container, a discharge valve, means for controlling saidvalve responsive to at least one pre' determined physical condition associated with the generation of steam within said boiler, and passage means con necting said discharge valve to the bottom end of said con- 7 tainer.

i 2. Electrode steam boiler apparatus as claimed in claim 1 in which saidcontainer is a cylinder of which the axis of generation is vertical.

3. Electrode steam boiler apparatus comprising a boiler, steam generating electrodes in the boiler, a closed container having an upper end and a lower end, said container having a volume substantially equal to the volume of water contained between minimum and maximum levels of said boiler during normal operation, passage means connecting the upper end of said container to said boiler at a point below the minimum water level during normal operation, a feed tank, second passage means connecting said feed tank to the lower end of said container, a feed pump in said second passage means arranged to pump water from the feed tank to the container, third passage means connecting said feed tank to the lower end of said container, and a discharge valve in said third passage means, and means for controlling saidvalve responsive to at least one predetermined physical condition associated with the generation of steam within said boiler.

' 4. Electrode steamboiler apparatus comprising an electrode steam boiler, a closed container having an upper end and a lower end, said container having a volume substantially equal to the volume of water contained between minimum and maximum levels of said boiler during normal operation, a pipe connecting the upper end to the boiler at a point below the minimum water level during normal operation, means for pumping cold water from a Water source into the lower end of said container and means responsive to at least one predetermined physical condition associated with the generation of steam within said boiler for bleeding cold water from the lower end of said container to a point at atmospheric pressure.

ANTHONY BARTIS, Examiner. 

4. ELECTRODE STEAM BOILER APPARATUS COMPRISING AN ELECTRODE STEAM BOILER, A CLOSED CONTAINER HAVING AN UPPER END AND A LOWER END, SAID CONTAINER HAVING A VOLUME SUBSTANTIALLY EQUAL TO THE VOLUME OF WATER CONTAINED BETWEEN MINIMUM AND MAXIMUM LEVELS OF SAID BOILER DURING NORMAL OPERATION, A PIPE CONNECTING THE UPPER END TO THE BOILER AT A POINT BELOW THE MINIMUM WATER LEVEL DURING NORMAL OPERATION, MEANS FOR PUMPING COLD WATER FROM A WATER SOURCE INTO THE LOWER END OF SAID CONTAINER AND MEANS RESPONSIVE TO AT LEAST ONE PREDETERMINED PHYSICAL CONDITION ASSOCIATED WITH THE GENERATION OF STEAM WITHIN SAID BOILER FOR BLEEDING COLD WATER FROM THE LOWER END OF SAID CONTAINER TO A POINT AT ATMOSPHERIC PRESSURE. 